The present invention relates to an Ultra-Low-Profile Small Computer System Interface (SCSI) bus terminator. SCSI bus terminators are well known in the art. In small computer systems, a SCSI bus is employed to allow data communication between a CPU and peripheral devices such as disk drives, printers or other devices. Terminators are connected at each end of the bus to supply a matched termination impedance, and in the case of regulated terminators, to supply a constant voltage to the various signal lines comprising the bus.
Initially, SCSI terminators were purely passive devices. The most common terminator circuit comprised a 220 .OMEGA. resistor and a 330 .OMEGA. resistor connected in series between a +5 V termination power supply and ground, with the signal line being connected at the junction of the two resistors. Over time, improvements to the SCSI standard have been made, and several alternate termination circuits are now widely used. In addition to the passive 220/330 terminator, there are now regulated voltage terminators which incorporate a voltage regulator within the terminator apparatus and supply a regulated voltage directly to the signal lines through a 110 .OMEGA. termination resistor. There are also active terminators for use in SCSI systems employing active signal line deassertion (ADR), as well as passive low voltage differential terminators (LVD), and signal line increased current kicker terminators (SLICK.RTM.) which supply additional current to the ACK and REQ signal lines in order to avoid false data transitions. The various terminator circuits available today have specific advantages for particular applications, and the particular circuit employed will generally be dictated by the application.
Irrespective of which particular termination circuit is employed in a given SCSI application, the continued drive for miniaturization of computer components has created pressure to minimize the physical envelope taken up by SCSI terminators. Various packaging schemes have been devised to reduce the external dimensions of SCSI terminators generally. Both internal mount and external mount terminators have been developed in order to meet the space limitations imposed by the packaging requirements of the particular computer system into which a terminator is to be installed. Each type raises particular packaging demands which must be addressed in order to design an effective SCSI terminator. In general, an internal mount terminator will connect to a female connector header soldered to a printed circuit board. An external mount terminator will plug into an electrical connector mounted in a wall of the chassis of a computer or external peripheral device. While it is always desirable to reduce the overall dimensions of any terminator, the ever shrinking packaging of computer systems places the highest premium on reducing the space occupied by internal mount terminators.
Some common elements found in both internal and external mount terminators include a connector for connecting the terminator to the SCSI bus, a printed circuit board on which the various termination component are mounted, and a housing enclosing the terminator components. Often with internal mount terminators, a portion of the SCSI bus will be traced on the surface of a printed circuit board and each signal line will be soldered to a single pin within a connector header. The terminator's connector will connect to the header, and through the header connect the signal lines of the bus to the terminator printed circuit board. Often the printed circuit board on which the connector header is mounted will be near a wall of the chassis enclosing the device into which the terminator is to be mounted. In this case there will be very limited vertical space above the header in which to mount the terminator. (Note: the direction described here as "vertical" is completely arbitrary and could easily be replaced by any other direction depending on the orientation of the device). Due to this lack of vertical space, the terminator connecting to the header must have a very short height component.
A prior art terminator packaged to meet such requirements is shown in FIG. 1. The terminator package includes a male IDC connector 10 for connecting to a female connector header soldered to a printed circuit board which is not shown. The IDC connector 10 is connected to a first end of a short section of flexible ribbon cable 12, and the opposite end of the ribbon cable is joined to a male IDC ribbon header 14. The ribbon header 14 includes pins which are soldered to a horizontal printed circuit board located beneath a plastic cover 16. The printed circuit board beneath the cover contains the actual termination circuitry of the terminator which is connected to the various conductors of ribbon cable 12 via the male IDC header 14.
The prior art terminator of FIG. 1 presents a low vertical profile in that the height of the entire assembly is no greater than the height of the male IDC connector 10. Thus the device of FIG. 1 is well adapted for applications where a SCSI terminator is to be mounted within a device chassis where there is limited room between the SCSI bus header and a wall of the chassis or some other physical obstruction. A disadvantage with the FIG. 1 device, however, is that it is comprised of a fairly large number of component parts which must be individually assembled. The complexity of the componentry comprising the terminator has the undesirable effect of raising the manufacturing cost of the device. Another disadvantage with the device of FIG. 1 is that although low in profile, the entire assembly nonetheless occupies a significant amount of space albeit in a fairly low horizontal plane.
What is needed is a SCSI terminator having an improved ultra-low-profile which consumes no more vertical space than a typical IDC connector. Such a terminator package must be easily assembled, and include only a small number of individual parts. Furthermore, the improved terminator should be relatively inexpensive to manufacture and should consume only a minimal amount of space in the horizontal plane in addition to being low in profile. Finally, the improved terminator package should include a housing which is readily adapted for use as an external mount terminator which can be plugged directly into an exterior connector mounted on the outside of a SCSI device. The connector portion of the improved terminator should further be configured as a high density connector having either fifty or sixty-eight contact pins spaced on 0.050" centers.